1. Field of the Invention
The present invention relates to an image forming apparatus for forming an image on a recording material using an electrophotographic system and, in particular, to a development device and a process cartridge applied to the image forming apparatus.
2. Description of the Related Art
In an image forming apparatus such as a printer using an electrophotographic image forming system (an electrophotographic process), an electrophotographic photosensitive member (hereinafter referred to as a “photosensitive member”) acting as an image carrier is uniformly charged, and the charged photosensitive member is selectively exposed to form an electrostatic image on the photosensitive member. The electrostatic image formed on the photosensitive member is visualized as a toner image by a toner as a developer. The toner image formed on the photosensitive member is transferred to a recording paper or a recording material such as a plastic sheet and the toner image transferred to the recording material is subjected to heat and pressure to be fixed to the recording material, thereby recording an image.
In general, such an image forming apparatus requires the supply of a developer and the maintenance of various process units. For the purpose of facilitating the supplying work of the developer and the maintenance of various process units, a photosensitive member, a charging unit, a developing unit, and a cleaning unit are integrated into a frame member to form a cartridge, and thereby a process cartridge detachable from the image forming apparatus main body is put into practical use. A process cartridge system can provide an image forming apparatus excellent in usability.
In recent years, a color image forming apparatus for forming a color image using a plurality of color developers has come into wide use. As the color image forming apparatus, an inline image forming apparatus is known in which a photosensitive member corresponding to each of image forming operations using a plurality of color developers is arranged in a row along a moving direction of the surface of a member to be transferred to which the toner image is transferred. Some inline color image forming apparatuses arrange in row a plurality of photosensitive members in the direction (in the horizontal direction, for example) intersecting with the vertical direction (direction of gravity). The inline system image forming system is advantageous in that it can easily cope with demand for increasing an image forming speed and developing to a multifunction printer.
Some image forming apparatuses arrange photosensitive members under an intermediate transfer member acting as the member to be transferred or a recording material carrier conveying a recording material acting as the member to be transferred.
If the photosensitive members are arranged under the intermediate transfer member or the recording material carrier, a fixing device and a development device (or an exposure device), for example, can be arranged in a separate position with the intermediate transfer member or the recording material carrier sandwiched in the image forming apparatus main body. This brings the advantage of the development device (or the exposure device) being insusceptible to heat.
As described above, if the photosensitive members are arranged under the intermediate transfer member or the recording material carrier, a developer storage portion in the development device may need to supply a developer to a developing roller (or a developer carrier) or a supply roller (a supplying member) contrary to gravity.
Japanese Patent Application Laid-Open No. 2003-173083 discusses a method of bringing a receiving sheet into contact with the lower side of the supplying member, as a method for supplying a developer to the supplying member. According to the method, the receiving sheet prevents the developer adhering to the supplying member from falling due to gravity and prevents the developer supplied to the developer carrier from decreasing, so that lowering of the density of a solid image is prevented.
Japanese Patent Application Laid-Open No. 2009-222931 discusses a method in which a developer is conveyed to the lower surface of a supplying member by a conveyance member provided under the supplying member and the toner is inhibited from coagulating in the development chamber lying above the developer storage portion.
However, in the method of supplying the developer discussed in Japanese Patent Application Laid-Open No. 2003-173083, if an image low in a printing ratio is continuously output, the developer is retained and coagulated between the supplying member and the receiving sheet, so that image quality deterioration such as density ununiformity may occur.
In a configuration of Japanese Patent Application Laid-Open No. 2009-222931, the conveyance member needs to be added in addition to the supplying member in the development chamber to complicate the configuration of an apparatus. The friction between the developer and the conveyance member in the development chamber deteriorates the developer.